日照一次EF2级龙卷的环境场及雷达特征

Environmental field and radar characteristics of an EF2 scale tornado in Rizhao

利用常规观测资料、区域自动气象观测站加密观测资料、多普勒雷达资料和NCEP/NCAR 1°×1°再分析资料,对2019年8月16日发生在日照一次龙卷天气过程的天气形势、环境物理量和涡旋特征进行了分析。结果表明:地面β中尺度辐合线和高空冷涡是此次龙卷发生的主要影响系统,较湿的近地面层、较低的抬升凝结高度为龙卷的发生提供了有利的环境条件。地面辐合线上的γ中尺度涡旋在显著深厚湿对流潜势下触发了对流,较大的对流有效位能(convective available potential energy,CAPE)和较强的0~3 km垂直风切变有利于初生对流的发展、合并,形成超级单体风暴。龙卷发生时,超级单体风暴低层右前侧出现钩状回波、入流缺口。较强的风暴单体、深厚持久的中气旋、中气旋强中心和底部迅速下降并重合、气旋性涡旋加强、最大风切变跃增、多个时次体扫出现龙卷涡旋特征(tornadic vortex signature,TVS)是地面龙卷发生的主要特征。对龙卷风暴单体移动起主导作用的因子在不同时段有所不同,前期主要受平流的影响;风暴单体合并的过程中,风暴移动受传播和平流的共同影响;风暴单体完全合并后,引导气流对风暴的移动又起主要作用。

The synoptic situations,environmental physical parameters,and vortex signatures of a tornado process that occurred in Rizhao on 16 August 2019 are analyzed by using conventional observation data,data of densified regional automatic meteorological stations and Doppler weather radar,and NCEP/NCAR 1°×1°reanalysis data.The results are shown below.The meso-βscale convergence line and the northeast cold vortex are main synoptic systems,and the wet near-surface layer and low lifting condensation level provide favorable environmental conditions for the tornado.The meso-γscale vortices on the ground convergence line trigger convections under significant deep wet convective potential,and the larger CAPE(convective available potential energy),stronger 0-3 km vertical wind shear are conducive to the development and merging of convective initiation,which eventually leads to the formation of the supercell storm.The hook echo and inflow notch appear on the right front of the lower layer of supercell storm when the tornado occurs.The main echo characteristics of the tornado are strong storm cell,deep and long-lasting mesocyclone,the strong center and bottom of the mesocyclone descending rapidly and coinciding,the cyclonic vortex being strengthened,the maximum wind shear increasing sharply,and tornadic vortex signature(TVS)appearing in many times of radar volume scan.The factors that play a dominant role in controlling the movement of tornado storm cells are different in different periods:the movement of early storms is mainly affected by advection;during the merging of storm cells,the movement is affected both by propagation and advection;after the storm cells completely merge,the steering flow plays an important role in controlling the movement of storm.